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Loans and allowance for credit losses - Individually Assessed Allowance for Credit Losses for Collateral Dependent Loans (Details) - USD ($) $ in Thousands | Dec. 31, 2020 | Jan. 01, 2020 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
--- | --- | --- | --- | --- | ---
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |
Type of Collateral | $ 170,389 | $ 31,139 | $ 31,139 | $ 28,932 | $ 24,041
Individually assessed allowance for credit loss | 2,039 |  | 895 | 268 |
Commercial and industrial |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |
Type of Collateral | 14,748 |  | 4,805 | 5,348 | 4,461
Individually assessed allowance for credit loss | 373 |  | 241 | 3 |
Construction |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |
Type of Collateral | 58,477 |  | 10,194 | 9,729 | 7,135
Individually assessed allowance for credit loss | 95 |  | 0 | 0 |
Residential real estate | 1-to-4 family mortgage |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |
Type of Collateral | 19,220 |  | 3,112 | 3,428 | 3,197
Individually assessed allowance for credit loss | 0 |  | 8 | 7 |
Residential real estate | Residential line of credit |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |
Type of Collateral | 10,534 |  | 752 | 811 | 944
Individually assessed allowance for credit loss | 9 |  | 9 | 0 |
Residential real estate | Multi-family mortgage |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |
Type of Collateral | 7,174 |  | 544 | 566 | 434
Individually assessed allowance for credit loss | 0 |  | 0 | 0 |
Commercial real estate | Owner occupied |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |
Type of Collateral | 4,849 |  | 4,109 | 3,132 | 3,558
Individually assessed allowance for credit loss | 30 |  | 238 | 53 |
Commercial real estate | Non-owner occupied |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |
Type of Collateral | 44,147 |  | 4,621 | 4,149 | 2,817
Individually assessed allowance for credit loss | 1,531 |  | 399 | 205 |
Consumer and other |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |
Type of Collateral | 11,240 |  | 3,002 | 1,769 | $ 1,495
Individually assessed allowance for credit loss | 1 |  | $ 0 | $ 0 |
Real Estate |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |
Type of Collateral | 16,832 |  |  |  |
Real Estate | Commercial and industrial |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |
Type of Collateral | 0 |  |  |  |
Real Estate | Construction |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |
Type of Collateral | 3,877 |  |  |  |
Real Estate | Residential real estate | 1-to-4 family mortgage |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |
Type of Collateral | 226 |  |  |  |
Real Estate | Residential real estate | Residential line of credit |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |
Type of Collateral | 1,174 |  |  |  |
Real Estate | Residential real estate | Multi-family mortgage |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |
Type of Collateral | 0 |  |  |  |
Real Estate | Commercial real estate | Owner occupied |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |
Type of Collateral | 3,391 |  |  |  |
Real Estate | Commercial real estate | Non-owner occupied |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |
Type of Collateral | 8,164 |  |  |  |
Real Estate | Consumer and other |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |
Type of Collateral | 0 |  |  |  |
Financial Assets and Equipment |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |
Type of Collateral | 1,728 |  |  |  |
Financial Assets and Equipment | Commercial and industrial |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |
Type of Collateral | 1,728 |  |  |  |
Financial Assets and Equipment | Construction |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |
Type of Collateral | 0 |  |  |  |
Financial Assets and Equipment | Residential real estate | 1-to-4 family mortgage |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |
Type of Collateral | 0 |  |  |  |
Financial Assets and Equipment | Residential real estate | Residential line of credit |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |
Type of Collateral | 0 |  |  |  |
Financial Assets and Equipment | Residential real estate | Multi-family mortgage |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |
Type of Collateral | 0 |  |  |  |
Financial Assets and Equipment | Commercial real estate | Owner occupied |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |
Type of Collateral | 0 |  |  |  |
Financial Assets and Equipment | Commercial real estate | Non-owner occupied |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |
Type of Collateral | 0 |  |  |  |
Financial Assets and Equipment | Consumer and other |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |
Type of Collateral | 0 |  |  |  |
Collateral Pledged |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |
Individually assessed allowance for credit loss | 1,687 |  |  |  |
Collateral Pledged | Commercial and industrial |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |
Individually assessed allowance for credit loss | 117 |  |  |  |
Collateral Pledged | Construction |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |
Individually assessed allowance for credit loss | 0 |  |  |  |
Collateral Pledged | Residential real estate | 1-to-4 family mortgage |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |
Individually assessed allowance for credit loss | 0 |  |  |  |
Collateral Pledged | Residential real estate | Residential line of credit |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |
Individually assessed allowance for credit loss | 9 |  |  |  |
Collateral Pledged | Residential real estate | Multi-family mortgage |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |
Individually assessed allowance for credit loss | 0 |  |  |  |
Collateral Pledged | Commercial real estate | Owner occupied |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |
Individually assessed allowance for credit loss | 30 |  |  |  |
Collateral Pledged | Commercial real estate | Non-owner occupied |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |
Individually assessed allowance for credit loss | 1,531 |  |  |  |
Collateral Pledged | Consumer and other |  |  |  |  |
Financing Receivable, Allowance for Credit Loss [Line Items] |  |  |  |  |
Individually assessed allowance for credit loss | $ 0 |  |  |  |

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